A stent is commonly used as a tubular structure left inside the lumen of a vessel or duct of the body, in order to relieve an obstruction in the lumen or duct. Commonly, stents are inserted into the lumen in their unexpanded form; the stents are then expanded on their own (or with the aid of a second device) in situ at the obstruction. A typical method of expansion occurs through the use of a catheter-mounted stent on an angioplasty balloon, which balloon is inflated within the stenosed vessel or body passageway. This inflation causes the obstructions of the vessel associated with the wall components of the vessel to compress. Thereafter, the stent holds the obstruction in place at the vessel wall, and an enlarged lumen is obtained.
It is fairly commonly believed that usage of a stents is a technology transforming the type of therapy used against stenosis of a lumen. That is, in the absence of a using a stent, (in other words, when a balloon used alone) restenosis often occurs, as a result of elastic recoil of the stenotic lesion away from the vessel wall. So, stents have been hailed as a breakthrough in the use of science to improve medicinal therapies.
Although a number of stent designs have been created, the designs of these stents have exhibited a number of limitations, such as a general restriction on the dimension of the stent. For instance, typical stents have been limited to a pair of generally rigid ends (approx. 8 mm) and a flexible middle section (anywhere from about 7 mm to about 21 mm). This device is formed of multiple parts and is not continuously flexible along the longitudinal axis. Other stent designs with rigid segments and flexible segments have also been described.
Other stents are described as longitudinally flexible, but consist of a plurality of cylindrical elements connected by flexible members. This design has at least one important disadvantage, for example, according to this design, protruding edges occur when the stent is flexed around a curve raising the possibility of inadvertent retention of the stent on plaque deposited on arterial walls. This may cause the stent to embolize or more out of position and further cause damage to the interior lining of healthy vessels. Thus, balloon expandable stents known in the art, generally compromise axial flexibility to permit expansion and provide overall structural integrity.
However, it is further more desirable to be able to vary the flexibility of the stent along its length. In other words, it may be more desirable to have a stiffer stent at the proximal end and a more flexible stent at the distal end, or vice versa. To be able to vary the flexibility of the stent along its length could provide for emplacement of the proximal end in a narrower or more tortuous coronary artery, while stabilizing the stent at its proximal end. Or, it might be desirable to vary the flexibility in the center of the stent in order to achieve a bend of a particular coronary artery. If the stent could be produced reliably and quickly, it may be possible to examine the patient, determine the degree of tortuousity of the patient's coronary arteries, and then construct the stent to tailor to the patient.